Suppress specified packages' warnings through CLI

[mee7ya]

Problem

Sometimes, working on less than all local packages, I don't want to see warnings from packages I currently do not work with. Additionally, having less warnings in total makes tools like rust-analyzer run faster, since they don't have process "uninteresting" errors

Currently, cargo will output all warnings produced by rustc from locally defined packages. And, as far as I understand, the only way to disable those warnings is by using #[allow(warnings)] attribute in lib.rs, which is not convenient

Proposed Solution

Add --allow-warnings argument to cargo check, cargo build, etc. to suppress output of specified packages' warnings

Notes

Possible implementation db966b5

[weihanglo]

There is already an unstable build.warnings config. Going to close in favor of the tracking issue #14802

Let us know if there is a reason to keep this open separately.

[mee7ya]

I don't want to suppress warnings from all packages.

E.g., Cargo.toml

[package]
name = "rust-random"
version = "0.1.0"
edition = "2024"

[dependencies]
some-pkg = { path = "some-pkg" }

Intentionally adding some warnings to rust-random and some-pkg leads to:

$ cargo check                                                      
warning: unused import: `std`
 --> some-pkg/src/lib.rs:1:5
  |
1 | use std;
  |     ^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: `some-pkg` (lib) generated 1 warning (run `cargo fix --lib -p some-pkg` to apply 1 suggestion)
warning: unused variable: `a`
 --> src/main.rs:4:9
  |
4 |     let a = 0;
  |         ^ help: if this is intentional, prefix it with an underscore: `_a`
  |
  = note: `#[warn(unused_variables)]` on by default

warning: `rust-random` (bin "rust-random") generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s

Each package generates 1 warnings, using the CARGO_BUILD_WARNINGS=allow

$ CARGO_BUILD_WARNINGS=allow cargo +nightly check -Zwarnings
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.21s

Suppresses both some-pkg and rust-random. How do I suppress warnings only from some-pkg? With the commit from notes section I can do

$ cargo check --allow-warnings some-pkg
warning: unused variable: `a`
 --> src/main.rs:4:9
  |
4 |     let a = 0;
  |         ^ help: if this is intentional, prefix it with an underscore: `_a`
  |
  = note: `#[warn(unused_variables)]` on by default

warning: `rust-random` (bin "rust-random") generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.21s

I still get warnings from rust-random, but I don't from some-pkg

[weihanglo]

Ah I see. Thanks for the clarification.

[weihanglo]

I updated the title to focus on the problem instead of a warning.

[weihanglo]

I am not sure if I framed the title correctly. I guess the problem is more like

• I want to see warnings only from the package I currently work on

or to extend a bit more

• I know my local crates have a lot of warnings, but I only want to see a subset of them that I can consume and deal with

Or I saw some requests from some AI agentic tool users

• I'd like tools to have smaller scope and more concise diagnostics so I can save my tokens and agentic tools can understand more precisely

Those above are quite similar requests. I'd like to understand the scenario more on why.

[mee7ya]

I apologise for my confusing description.

This would the best way to describe the issue:

I know my local crates have a lot of warnings, but I only want to see a subset of them that I can consume and deal with

I have a crate that is created by code generator. It contains 100s of structs. At the time of working on that crate the latest rust version was 1.88.* . After some time rust 1.89.* releases which introduces a mismatched lifetime syntaxes lint. Now the same crate produces 4000+ warnings. For one reason or the other, I can't work on fixing code generator yet, but those warnings flood output of check, build and etc. It makes rust-analyzer's each run very slow (around 30 seconds). In manual cargo runs I have to skip warnings from this problematic crate to find warnings from crates I can fix. In this particular case, I can use RUSTFLAGS="-Amismatched_lifetime_syntaxes", but this will also suppress the exact warning from all crates.

Since you mentioned the agentic tools, I'd guess having too many warnings can affect them too.

[epage]

For one reason or the other, I can't work on fixing code generator yet, but those warnings flood output of check, build and etc.

How long is this "yet". At first I took this issue to be about focusing your view as you work through a large backlog. However, this makes it sound like you expect to keep it this way for a bit. In that case, I'd add a #![expect(…)] in that library.